The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. All references described herein are incorporated by reference in their entireties into the current application.
Chitosan is a linear polysaccharide comprising primarily beta-(1-4)-polysaccharide of D-glucosamine. Chitosan is structurally similar to cellulose, except that the C-2 hydroxyl group in cellulose is substituted with a primary amine group in chitosan. Chitosan is produced commercially by deacetylation of chitin, which is the structural element in the exoskeleton of crustaceans such as crabs, shrimp, etc. and cell walls of fungi, etc.
Historically, the exploration of chitosan has been focused on medical and pharmaceutical applications, due to the inherent biocompatibility and reactive functionality of chitosan. Examples in these respects include using chitosan as an implantable/injectable material, a hemostatic agent, a wound-healing component, etc.
Much of the industrial interest in chitosan however relates to its ability to generate viscous and elastic (hydro)gels via physical or chemical interactions. To date, the most common crosslinkers used with chitosan are dialdehydes such as glyoxal and in particular glutaraldehyde. The aldehyde groups form covalent imine bonds with the amino groups of chitosan, due to the resonance established with adjacent double ethylenic bonds, even though links with hydroxyl groups cannot be completely excluded. Other covalent crosslinkers include diethyl squarate, oxalic acid, and genipin, where the underlying mechanisms of the crosslink remain incompletely elucidated. However, several health issues are associated with the use of these compounds to crosslink chitosan.
The application of chitosan in the oil and gas industry has also been explored to a certain degree. For example, U.S. Pat. No. 7,007,752 discloses a method of using derivatised chitosan with an oxidized polysaccharide such as starch to form a well treatment fluid; U.S. Pat. No. 6,764,981 discloses a method of using oxidized chitosan and acrylamide-based polymer to treat a subterranean formation; U.S. Pat. No. 7,322,414 discloses a crosslinkable-polymer composition comprising an aqueous fluid, a chitosan-reacting polymer, chitosan and a gelation-retarding additive. The entire contents of these patents are incorporated by reference into the current application.
However, none of the references employs chitosan as the primary ingredient in the treatment fluid. Instead, chitosan has been used mainly as an additive or crosslinker in the treatment fluid. There remains a need to further explore compositions and methods that use chitosan as the primary ingredient in a fluid for treating a subterranean formations penetrated by a wellbore, i.e. a chitosan-based treatment fluid for use in the oil and gas industry.